Pore-fluid pressure is known to play a key role in activating of geological faults at a wide range of scale. Elevated fluid pressure within fractures or pores changes mechanical conditions, resulting in fluid-induced seismicity. This paper presents an experimental technique to reactivate fracture plane induced by elevated pore pressure. Fracture plane of Kimachi sandstone was reactivated through a series of incremental sequence of pore pressure under stress conditions controlled by true triaxial test apparatus. Of particular interest is the relationship between pore pressure evolution and mechanical response within the fractured specimen during reactivation. Stress, displacement, and permeability exhibited instantaneous changes at an elevated pore pressure. Hysteresis effect and anisotropic measurements of displacement indicate fracture reactivation of the specimen.

1 Introduction

Pore-fluid pressure is known to play a key role in activating of geological faults at a wide range of scale. One of the main factors causing the fault reactivation is increases in pore fluid pressure which generally decreases in effective stress and shear strength. Pore pressure-induced dynamic strains could change mechanical conditions of a critically stressed fault, resulting in seismic waves which sometimes trigger large earthquake. Understanding the hydromechanical interactions associated with fault reactivation in the shallow crust is important for many geoengineering applications, such as evaluating micro-seismicity impacts on impounding reservoirs, extracting shale gas through fracture stimulation, and enhancing geothermal systems (Valko & Economides 1995).

Various field observations have been conducted to investigate fault behavior during reactivation induced by elevated pore pressure. Guglielmi et al. (2015) has been directly measured spatial displacements of the fault during reactivation induced by pore pressure injection. Their in-situ observation showed the movement of the existing faults (i.e., opening and sliding) and its correlation with seismic events. In field experiments at a granite quarry, Cornet et al. (2003) measured displacement-injection pressure hysteresis via hydraulic jacking tests to study the effects of threshold injection pressure on fracture aperture.

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